This invention relates to the field of optical coupling systems.
One of the most common optical connections is between an optical fiber end and a collimating lens, such as spherical or aspherical lenses and/or graded index (GRIN) lenses. Grin lenses are produced under the trade name xe2x80x9cSELFOCxe2x80x9d; the mark is registered in Japan and owned by the Nippon Sheet and Glass Co. Ltd.
A common coupler system comprises a sleeve in which a fiber end within a supporting ferrule is joined to a lens by attaching the sides of the ferrule and the lens to the interior bore of the sleeve.
Another common practice is to couple an optical fiber to a lens by placing the optical fiber into a ferrule or fiber tube and joining an end face of the tube directly to a face of the lens by applying a layer of epoxy between them. A direct ferrule to lens epoxy connection facilitates alignment of the coupled elements and provides a uniform joint. However, epoxy is not completely transparent or uniform to transmission. Transmission of light though the epoxy layer results in some loss.
To couple an optical fiber end to an optical element, such as a lens, there are three positioning variables: the spacing between the elements, the coupling point relative to the optical axis, and the coupling angle. Common coupling techniques do not provide a convenient method of adjusting the spacing between the elements, or the coupling angle.
It is often desired to make a coupling with a precise predetermined distance between elements, which is not possible with a direct epoxy connection. Typically this is accomplished by fixing the elements with the desired separation between them on a substrate with adhesive. It is difficult to establish an exact separation, or alignment and angular positioning by this method.
Substantial coupling losses may occur between a fiber end and a collimating lens when the distance or gap between these elements is significant. This is particularly the case for long working distance collimators having increased focal lengths. It is one aspect of this invention to reduce this unwanted coupling loss. In addition to a controlled coupler spacing, a correct coupling angle is critical in some configurations for a low loss coupling. A gap between the fiber end and the collimating lens causes a beam of light propagating from the fiber end to the collimating lens to be shifted downwards or upwards depending on the slant of the fiber facet. Hence, in order to achieve an efficient coupling between the fiber and the lens, it is known to provide the fiber at an appropriate angle with respect to the optical axis of the lens. However, this increases the package size for such a coupling system.
It is desired to provide a coupling system which provides a reliable means for coupling between optical elements. It is further desired to provide a coupling system which is unimpeded by transmission through an epoxy layer.
It is an object of this invention to provide an optical coupling system having an in-line or coaxial arrangement between an optical axis of a collimating lens and a center of a waveguide.
Another object of this invention is to provide an optical coupling arrangement with low coupling losses and a small coupler package size.
In accordance with the invention there is provided, an optical light coupling system comprising: an optical waveguide having a slanted end face; a lens for receiving a beam of light from the optical waveguide, wherein an optical axis of the lens defines a line extending through a center of a light guiding portion of the optical waveguide; and a powerless non-birefringent element disposed between the optical waveguide and the lens along the line defined between the optical axis of the lens and the center of the light guiding portion of the optical waveguide for maintaining a substantially linear propagation of the beam of light along the line, wherein the powerless non-birefringent element has a first end face facing an end face of said optical waveguide and defining an angle therebetween, and a second end face facing the lens.
In accordance with the invention, there is further provided, an optical coupling arrangement comprising: an optical fiber having a slanted end face; a lens for receiving a beam of light from the optical fiber, the lens and the slanted end face of the optical fiber being in a spaced relationship along a line defined between an optical axis of the lens and a center of a core of the optical fiber such that the slanted end face of the optical fiber is disposed in the focal plane of the lens; and a powerless non-birefringent optical element being optically coupled with the optical fiber and the lens and disposed therebetween for ensuring that a center of the beam substantially follows the line, the element having a first and a second end face, the first end face facing the slanted end face of the optical fiber, the first end face and the slanted end face of the optical fiber defining an angle therebetween, and the second end face facing the lens.
The invention further provides an optical light coupling system comprising: an optical fiber having a core and a slanted end face; a collimating lens for receiving a beam of light from the optical fiber; and a light transmissive element disposed between said optical fiber and the collimating lens, said light transmissive element having a substantially same refractive index as the core of the fiber for maintaining a substantially linear propagation of the beam of light, said light transmissive element having a first end face for mating with the optical fiber and being complementary thereto and a second end face for coupling with the lens, said light transmissive element, said collimating lens, and said optical fiber are co-axial.